Earthquake and Tsunami Good for Beaches — Seawalls, Not So much

A new study which received a health dose of serendipity has revealed that earthquakes and tsunamis may actually have a huge environmental benefit on beaches.

Science is awesome

There are many reasons why I love science, and this is just another one to add to the pile. Scientists from Universidad Austral de Chile and UC Santa Barbara’s Marine Science Institute (MSI) were studying the ecological impact man-made armouring such as seawalls and rocky revetments had on sandy beaches in Santa Barbara and south central Chile. Naturally, to do so, the scientists were out on the beaches surveying nine sandy beaches along the coasts of Maule and Bíobío in late January, 2010.

Guess what happened in February.

Yep, that’s right. An 8.8 magnitude earthquake struck and was followed by a devastating tsunami. This earthquake is recorded as the sixth largest to be recorded by a seismograph. Horribly, 525 lives were stolen and another 25 went missing.

But out of the tragedy comes this serendipitous story of scientific discovery.

This March 2010 photograph of the beach at Punta Lavapie reveals the extent of the uplift — these former subtidal rocky bottoms were completely submerged in water — at all times — prior to the Maule earthquake and tsunami.

For the environment, earthquake = good?

The results of their research have been published in the most recent edition of the journal PLoS ONE and show that flora and fauna return to beaches they have long been absent from in the wake of an earthquake such as the 2010 Chilean earthquake.

“So often you think of earthquakes as causing total devastation, and adding a tsunami on top of that is a major catastrophe for coastal ecosystems. As expected, we saw high mortality of intertidal life on beaches and rocky shores, but the ecological recovery at some of our sandy beach sites was remarkable,” said Jenifer Dugan, an associate research biologist at MSI. ” Dune plants are coming back in places there haven’t been plants, as far as we know, for a very long time. The earthquake created sandy beach habitat where it had been lost. This is not the initial ecological response you might expect from a major earthquake and tsunami.”

For some beaches, the news wasn’t great. In some instances, beaches were drowned, especially where the tsunami exacerbated earthquake-induced subsidence. However, in some areas the uplift brought about as a result of the earthquake widened and flattened some beaches.

Naturally, the drowned beaches suffered high mortality of intertidal life, but the beaches which were widened were soon inundated with the return of plants and animals that had long disappeared as a result of coastal armouring.

“With the study in California and our study here, we knew that building coastal defense structures, such as seawalls, decreases beach area, and that a seawall results in the decline of intertidal diversity,” said lead author Eduardo Jaramillo, of Universidad Austral de Chile. “But after the earthquake, where significant continental uplift occurred, the beach area that had been lost due to coastal armoring has now been restored. And the re-colonization of the mobile beach fauna was under way just weeks after.”

Damage and debris from the February 2010 earthquake and tsunami strewn across the revetment and uplifted beach at Llico

And then the climate change/sea-level rise linkage

As with many stories these days, there is always a climate change/sea-level rise component. The same can be said for this most recent discovery. The responses of beaches varied dramatically, unsurprisingly considering the haphazard and uncaring damage inflicted by an earthquake and tsunami.

What the researchers also found though, focusing more on their research into man-made armouring of beaches, is that there can be devastating and long-lasting footprints carved into coastal ecosystems when humans try to reshape the beaches, and in turn may suffer the consequences of a tsunami-drowned beach.

“When someone builds a seawall, not only is beach habitat covered up with the wall itself, but, over time, sand is lost in front of the wall until the beach eventually drowns,” Dugan said. “The semi-dry and damp sand zones of the upper and mid intertidal are lost first, leaving only the wet lower beach zones. This causes the beach to lose diversity, including birds, and to lose ecological function. This is an underappreciated human impact on coastlines around the world, and with climate change squeezing beaches further, it’s a very serious issue to consider.”

Jaramillo elaborated, “This is very important because sandy beaches represent about 80 percent of the open coastlines globally. Also, sandy beaches are very good barriers against the sea level rise we are seeing around the world. It is essential to take care of sandy beaches. They are not only important for recreation, but also for conservation.”

Source: University of California, Santa Barbara
Image Source: Eduardo Jaramillo

2 thoughts on “Earthquake and Tsunami Good for Beaches — Seawalls, Not So much”

Leave a Comment

Your email address will not be published. Required fields are marked *

Scroll to Top